GAN with batch norm acting very weird, both discriminator and generator get zero loss - tensorflow

Question

I am training a DCGAN model with tensorflow.keras, and I added BatchNormalization layers in both generator and discriminator.
I train gan with following steps:
1. train discriminator with real images and images from generator(using generator.predict)
2. train adversarial network(compiled with discriminator.trainable=False)
Then I found that after a few rounds the training loss returned by train_on_batch() of both generator and discriminator goes to zero. But when I use test_on_batch() the loss is still huge for generator. And the generated images are all mess.
At first I thought that it is because in the 2.'s step mentioned above when training the adversarial network, the discriminator's input only containing fake images makes the batch normalization layers get different distribution as the 1.'s step when both fake & real images were fed.
But even if I removed all batch normalization layers in discriminator, the same problem still exists. Only when all batch normalization layers were removed the problem will disappear. Also I found out that existences of Dropout layers don't make a difference. I wondering why batch normalization can cause such problem, even if in generator fed with noises with same distribution.
# Model definition
class DCGAN_128:
def __init__(self, hidden_dim):
generator = M.Sequential()
generator.add(L.Dense(128 * 8 * 8, input_shape=[hidden_dim]))
generator.add(L.Reshape([8, 8, 128]))
generator.add(L.UpSampling2D()) # [8, 8, 128]
generator.add(L.Conv2D(128, kernel_size=3, padding="same")) # [16, 16, 128]
generator.add(L.LayerNormalization()) # 4
generator.add(L.ReLU())
generator.add(L.UpSampling2D()) # [32, 32, 128]
generator.add(L.Conv2D(64, kernel_size=5, padding="same")) # [32, 32, 64]
generator.add(L.LayerNormalization()) # 8
generator.add(L.ReLU())
generator.add(L.UpSampling2D()) # [64, 64, 128]
generator.add(L.Conv2D(32, kernel_size=7, padding="same")) # [64, 64, 32]
generator.add(L.LayerNormalization()) # 12
generator.add(L.ReLU())
generator.add(L.UpSampling2D()) # [128, 128, 32]
generator.add(L.Conv2D(3, kernel_size=3, padding="same", activation=A.sigmoid)) # [128, 128, 3]
discriminator = M.Sequential()
discriminator.add(L.Conv2D(32, kernel_size=5, strides=2, padding="same", input_shape=[128, 128, 3]))
discriminator.add(L.LeakyReLU())
# discriminator.add(L.Dropout(0.25)) # [64, 64, 32]
discriminator.add(L.Conv2D(64, kernel_size=3, strides=2, padding="same"))
# discriminator.add(L.BatchNormalization(epsilon=1e-5)) # 4
discriminator.add(L.LeakyReLU())
# discriminator.add(L.Dropout(0.25)) # [32, 32, 64]
discriminator.add(L.Conv2D(128, kernel_size=3, strides=2, padding="same"))
discriminator.add(L.LayerNormalization()) # 8
discriminator.add(L.LeakyReLU()) # [16, 16, 128]
discriminator.add(L.Dropout(0.25))
discriminator.add(L.Conv2D(256, kernel_size=3, strides=2, padding="same"))
discriminator.add(L.LayerNormalization()) # 12
discriminator.add(L.LeakyReLU()) # [8, 8, 256]
discriminator.add(L.Dropout(0.25))
discriminator.add(L.Conv2D(512, kernel_size=3, strides=2, padding="same"))
discriminator.add(L.LeakyReLU()) # [4, 4, 512]
discriminator.add(L.Flatten())
discriminator.add(L.Dense(1, activation=A.sigmoid))
self.model_gen = generator
self.model_dis = discriminator
self.adv_input = L.Input([hidden_dim])
self.adv_output = discriminator(generator(self.adv_input))
self.model_adversarial = M.Model(self.adv_input, self.adv_output)
# Training
dcgan = hidden_dim = 100
DCGAN_128(hidden_dim)
data_loader = AnimeFacesLoader([128, 128])
batch_size = 32
n_rounds = 40000
dis_model = dcgan.model_dis
gen_model = dcgan.model_gen
adv_model = dcgan.model_adversarial
gen_model.summary()
adv_model.summary()
dis_model.compile(Opt.Adam(0.0002), Lo.binary_crossentropy)
dis_model.trainable = False
adv_model.compile(Opt.Adam(0.0002), Lo.binary_crossentropy)
layer_outputs = [layer.output for layer in dis_model.layers]
visual_model = tf.keras.Model(dis_model.input, layer_outputs)
for rounds in range(n_rounds):
# Get output images
if rounds % 100 == 0 and rounds > 0:
noise = np.random.uniform(-1, 1, [16, hidden_dim])
tiled_images = np.zeros([4*128, 4*128, 3]).astype(np.uint8)
generated_imgs = gen_model.predict(noise)
generated_imgs *= 256
generated_imgs = generated_imgs.astype(np.uint8)
for i in range(16):
tiled_images[int(i / 4)*128: int(i / 4)*128 + 128,
int(i % 4)*128: int(i % 4)*128 + 128, :] = generated_imgs[i, :, :, :]
Image.fromarray(tiled_images).save("Output/DCGAN/" + "rounds_{0}.jpg".format(rounds))
'''
layer_visualization = visual_model.predict(generated_imgs[:1])
for i in range(len(layer_visualization)):
plt.imshow(layer_visualization[i][0, :, :, 0])
plt.show()
'''
# train discriminator on real & fake images
real_imgs = data_loader.get_batch(batch_size)
real_ys = np.ones([batch_size, 1])
noise = np.random.uniform(-1, 1, [batch_size, hidden_dim])
fake_ys = np.zeros([batch_size, 1])
fake_imgs = gen_model.predict(noise)
imgs = np.concatenate([real_imgs, fake_imgs], axis=0)
ys = np.concatenate([real_ys, fake_ys], axis=0)
loss_dis = dis_model.train_on_batch(imgs, ys)
print("Round {}, Loss dis:{:.4f}".format(rounds, loss_dis))
loss_dis_test = dis_model.test_on_batch(imgs, ys)
print(loss_dis_test)
noise = np.random.uniform(-1, 1, [batch_size, hidden_dim])
fake_ys = np.ones([batch_size, 1])
loss_gen = adv_model.train_on_batch(noise, fake_ys)
print("Round {}, Loss gen:{:.4f}".format(rounds, loss_gen))
loss_gen_test = adv_model.test_on_batch(noise, fake_ys)
print(loss_gen_test)